tqm5200.c: fix warning: 'edid_buf' defined but not used

Commit 98e69567 "mpc52xx: add support for tqm52xx based board charon"
caused build warnings on some systems.  Fix these.

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Heiko Schocher <hs@denx.de>